Imaging and dosimetric characteristics of ⁶⁷ Cu

In recent years the use of beta-emitting radiopharmaceuticals for cancer therapy has expanded rapidly following development of therapeutics for neuroendocrine tumors, prostate cancer, and other oncologic malignancies. One emerging beta-emitting radioisotope of interest for therapy is ⁶⁷Cu (t_1/2: 2.6 d) due to its chemical equivalency with the widely-established positron-emitting isotope ⁶⁴Cu (t_1/2: 12.7 h). In this work we evaluate both the imaging and dosimetric characteristics of ⁶⁷Cu, as well as producing the first report of SPECT/CT imaging using ⁶⁷Cu. To this end, ⁶⁷Cu was produced by photon-induced reactions on isotopically-enriched ⁶⁸Zn at the Low-Energy Accelerator Facility (LEAF) of Argonne National Laboratory, followed by bulk separation of metallic ⁶⁸Zn by sublimation and radiochemical purification by column chromatography. Gamma spectrometry was performed by efficiency-calibrated high-purity germanium (HPGe) analysis to verify absolute activity calibration and establish radionuclidic purity. Absolute activity measurements corroborated manufacturer-recommended dose-calibrator settings and no radionuclidic impurities were observed. Using the Clinical Trials Network anthropomorphic chest phantom, SPECT/CT images were acquired. Medium energy (ME) SPECT collimation was found to provide the best image quality from the primary 185 keV gamma emission of ⁶⁷Cu. Reconstructed images of ⁶⁷Cu were similar in quality to images acquired using ¹⁷⁷Lu. Recovery coefficients were calculated and compared against quantitative images of ^99mTc, ¹⁷⁷Lu, and ⁶⁴Cu within the same anthropomorphic chest phantom. Production and clinical imaging of ⁶⁷Cu appears feasible, and future studies investigating the therapeutic efficacy of ⁶⁷Cu-based radiopharmaceuticals are warranted.